The present invention relates to a hybrid vehicle which is driven by the combination of driving force of the engine (internal combustion engine) and driving force of the driving motor (electric motor), and more particularly to a hybrid vehicle having a first transmission passage for transmitting engine driving force to driving wheels and a second transmission passage for transmitting motor driving force to the driving wheels.
For example, Japanese Patent No. 2942533 (see paragraphs [0015] to [0028]; FIGS. 1 and 2), which is also referred to as Patent Reference 1, discloses a known hybrid vehicle using driving force characteristics of the engine and the driving motor. This hybrid vehicle runs in a vehicle speed range lower than a predetermined vehicle speed (vehicle speed V1) by way of using a second transmission passage for transmitting the driving force of the driving motor to driving wheels, and runs in a vehicle speed range equal to or higher than the vehicle speed V1 by way of using the second transmission passage and a first transmission passage for transmitting the engine driving force to the driving wheels. Further, in a vehicle speed range closer to the maximum vehicle speed Vmax, the vehicle runs mainly by the first transmission passage for the engine. In this hybrid vehicle, the gear ratio of the first transmission passage is determined such that the maximum vehicle speed Vmax is achieved by driving force characteristics of the engine, and the second transmission passage and the first transmission passage are simple in structure without providing a variable gear ratio transmission. In the range around the maximum vehicle speed Vmax, the vehicle runs with the engine driving force being transmitted to the driving wheels using the first transmission passage.
Japanese Laid-open Patent Application No. 2004-123060 (see FIGS. 1, 2, 7, and 10), which is also referred to as Patent Reference 2, discloses a structure employing a first transmission passage and a second transmission passage as above, in a FF (i.e., Front-engine Front-wheel drive type) vehicle with a longitudinally arranged engine.
For example, as shown in FIG. 11A (corresponding to FIG. 7(A) of Patent Reference 2), a transmission mechanism 101 includes an engine-side input shaft 118 that is connected to the engine 113, a motor-side input shaft 119 that is connected to the driving motor 114, and an idle shaft 120 that is parallel to these input shafts 118, 119 and connected to the front wheels. The engine-side input shaft 118, the motor-side input shaft 119, and the idle shaft 120 are housed in a transmission casing while they are facing in the driving direction of the vehicle.
A crank shaft 122 of the engine 113 is connected to a rotor of a generator 125, which is further connected to the engine-side input shaft 118. The engine 113 drives the generator 125 as well as the engine-side input shaft 118. The engine-side input shaft 118 includes a drive shaft 118a connected to the crank shaft 122, and a driven shaft 118b to which an engine-side drive gear 130 is fixed. A clutch mechanism 136 is provided between the drive shaft 118a and the driven shaft 118b. 
Connected at the distal end of the motor shaft of the driving motor 114 is a motor-side input shaft 119. The distal end of the motor-side input shaft 119 is provided with a motor-side drive gear 131. In order to mesh with the engine-side drive gear 130 and the motor-side drive gear 131, the idle shaft 120 is provided with an engine-side idle gear 132 and a motor-side idle gear 133. Further, a pinion gear 134 as a final reduction pinion is provided at the distal end of the idle shaft 120, and a final gear 135 as a final reduction gear wheel is provided to mesh with the pinion gear 134. The final gear 135 is combined with deferential gears (not shown), so that the driving force transmitted from the engine-side input shaft 118 and the motor-side input shaft 119 to the idle shaft 120 is input to the final gear 135 and thereafter output to the right and left front drive shafts connected to the front wheels via the differential gears.
As shown in FIG. 11B (corresponding to FIG. 10(D) of Patent Reference 2), Patent Reference 2 discloses another embodiment of Patent Reference 2, in which a transmission mechanism 102 includes a clutch mechanism 136 that is built in between the engine-side idle gear 132 and the idle shaft 120.
As shown in FIG. 12A (corresponding to FIG. 10(A) of Patent Reference 2), a transmission mechanism 103 is also known, in which the driving motor 114 is arranged coaxially with the pinion gear 134 and further the idle shaft 120 and the motor-side input shaft 119 are also coaxially connected to the pinion gear 134 and the driving motor 114.
Also, as shown in FIG. 12B (corresponding to FIG. 10(B) of Patent Reference 2), a transmission mechanism 104 is known, in which the driving motor 114 is arranged coaxially with the engine 113 and further the engine-side input shaft 118 and the motor-side input shaft 119 are also coaxially connected to the engine 113 and the driving motor 114.
Further, as shown in FIG. 12C (corresponding to FIG. 10(C) of Patent Reference 2), a transmission mechanism 105 is known, in which the engine-side input shaft 118, the motor-side input shaft 119, and the idle shaft 120 are parallel to each other. The engine-side input shaft 118 is provided with a drive gear 184, and the motor-side input shaft 119 is provided with an intermediate gear 185 so as to mesh with the drive gear 184. In order to mesh with the intermediate gear 185, the idle shaft 120 is provided with an idle gear 186, so that the engine driving force and the motor driving force are transmitted to the idle shaft 120 via the idle gear 186.
According to the hybrid vehicle as disclosed in Patent Reference 1, when the vehicle runs or cruises in steady driving (cruise driving) requiring a low load, the vehicle runs in a series drive mode where the engine generates electricity and the driving motor drives the driving wheels, or alternatively, the vehicle runs by the engine driving force using the first transmission passage including a transmission mechanism having a relatively high reduction gear ratio (lowered gear ratio) that is set for realizing the maximum speed Vmax by the engine driving force.
However, the transmission efficiency of the driving force becomes relatively low in the series drive mode, and hence the fuel consumption of the vehicle may decrease accordingly. When the vehicle runs only by the engine driving force from the first transmission passage including the transmission mechanism having a lowered gear ratio, it is necessary for the vehicle to be driven with the lowered gear ratio that is set for realizing the driving force characteristics of the engine to achieve the maximum speed Vmax. This results in a greater change in the engine speed in accordance with vehicle speed at a steady drive. When the vehicle runs in the steady drive mode, it is not possible to select an arbitrary engine speed range for achieving improved fuel economy, and hence the fuel consumption of the vehicle decreases as a result.
Especially in the combination of the engine driving force and the motor driving force of a hybrid vehicle equipped with a large displacement engine, an excessive driving force is large. The fuel consumption may therefore decrease remarkably in the first transmission passage including the transmission mechanism having the lowered gear ratio as described above. Further, even if an output characteristic variable mechanism such as variable cylinder management is combined with a large displacement multi-cylinder engine so as to achieve improved fuel economy, the setting of this lowered gear ratio is insufficient to achieve advantages of the output characteristic variable mechanism for controlling cylinder deactivation drive for improved fuel economy.
Further, according to the FF vehicle equipped with the longitudinally arranged engine as shown in FIGS. 1 and 2 of Patent Reference 2, the longitudinal length of the engine room generally becomes long, and hence the weight of the vehicle increases accordingly. As a result of this, it is difficult to adapt this arrangement to a compact vehicle.
According to the transmission mechanisms 101, 102 as shown in FIGS. 11A and 11B, the idle shaft 120 is provided with the engine-side idle gear 132 and the motor-side idle gear 133, respectively, to transmit driving force to the driving wheels. This results in an increased size of the entire transmission mechanism, increased weight, decreased fuel consumption efficiency, increased cost, etc. Moreover, as the size of the transmission mechanism increases, the mounting space for the generator and the driving motor is limited so that the power generation capacity of the generator and the driving force of the driving motor are limited accordingly.
According to the transmission mechanism 103 as shown in FIG. 12A, since the speed of the driving motor 114 is reduced only by the pinion gear 134 and the final gear 135, a sufficient reduction gear ratio is not obtained and it becomes difficult to achieve effective driving of the vehicle during operation of the motor 114. Further, the layout of the engine 113 and the engine-side input shaft 118, and the layout of the driving motor 114, the motor-side input shaft 119, and the idle shaft 120 are limited to the center distance between the engine-side input shaft 118 and the idle shaft 120, which leads to a decrease in design freedom upon arrangement of the components of the transmission mechanism. As a result, it may be difficult to realize a layout design which allows a transmission mechanism for hybrid vehicles to be also mounted in a space within the engine room of an existing non-hybrid vehicle.
Further, according to the transmission mechanism 104 as shown in FIG. 12B, since the reduction gear ratio for the engine 113 is the same as the reduction gear ratio for the driving motor 114, it is difficult to realize effective driving of the vehicle using the engine driving force and the motor driving force, respectively.
Further, according to the transmission mechanism 105 as shown in FIG. 12C, the first transmission passage for transmitting the driving force of the engine 113 to the driving wheels has a three-stage reduction gears, i.e., between the driving gear 184 and the intermediate gear 185, between the intermediate gear 185 and the idle gear 186, and between the pinion gear 134 and the final gear 135. When compared with other transmission mechanisms 101, 102, 103, 104 as shown in FIGS. 11A, 11B, 12A, and 12B, the transmission mechanism 105 requires one more gear transmission than the other transmission mechanisms, which leads to deteriorated transmission efficiency and thus deteriorated fuel consumption efficiency. Moreover, in the case of an FF vehicle equipped with a transversely arranged engine, generally, the engine rotation direction is the same as the rotation direction of the driving wheels. However, the transmission mechanism 105 as shown in FIG. 12C has one more gear transmission than the other transmission mechanism. Therefore, it is necessary to change the engine rotation direction between a hybrid vehicle and a non-hybrid vehicle, which leads to an increase in manufacturing cost of the hybrid vehicle.
In view of the above disadvantages, the present invention seeks to provide a hybrid vehicle equipped with a transmission mechanism which is small and light-weighted and excellent in transmission efficiency.